That is a very bold statement. Do you want to back it up with some facts?
It's also a very wrong statement. Additional sources tell me that he spent some time chatting with them around a campfire (also suspected in the 1981 murders, but I don't believe confirmed). He met them on the trail.
This was cold and calculated. I suspect he went there knowing exactly what he was going to do, and didn't care who the victims were.
Don’t have anything for you, but that it is well known in the Law Enforcement/Forensics community.